A semiconductor sensing device such as a pressure sensing device has a semiconductor substrate with a pressure sensing bridge circuit comprising piezo-resistance elements formed on one side thereof. Further, a temperature sensing bridge circuit comprising resistance elements is also formed on the semiconductor substrate (JP-A-11-153503 and JP-A-10-281912).
A typical temperature sensing bridge circuit is shown in FIG. 7. As illustrated in FIG. 7, temperature sensing bridge circuits are generally manufactured by forming four resistance elements 9 to 12 having resistance values of R1 to R4 in a Wheatstone bridge.
More specifically, a power supply terminal T1 is connected with resistance elements 9 and 10, and a grounding terminal T2 is connected with resistance elements 11 and 12. At the same time, the resistance elements 9 and 12 are connected with each other at the junction T3, and the resistance elements 10 and 11 are connected with each other at the junction T4. The principle on which temperature is sensed by such a circuit is as follows.
It is assumed that the potentials at the junctions T3 and T4 in this bridge circuit are Vtp and Vtm, respectively. If Vtp=Vtm, the relation between the resistance values is expressed as R1×R3=R2×R4. This expression will be hereafter referred to as Ex. 1.
Conventionally, in general, the resistance elements 9 and 11 use an identical resistance type, and the resistance elements R2 and R4 use another identical resistance type B. The two resistance types A and B have different temperature characteristics from each other. That is, difference in resistance type means that one resistance type and the other resistance type are different in variation in resistance with temperature.
It is assumed that equilibrium, that is, Vtp=Vtm is obtained, for example, at room temperature (e.g., 25° C.). If the temperature further rises, the relation expressed by Ex. 1 does not hold, and becomes Vtp≠Vtm. As a result, a potential difference Ve is produced between junctions T3 and T4. Temperature can be sensed by variation in the potential difference Ve with temperature.
In case of a pressure sensing device, pressure information outputted from a pressure sensing circuit is corrected with the sensed temperature information. Thereby, temperature-compensated output values are produced.
However, in this temperature sensing bridge circuit, a potential difference Ve between the junctions is also produced by stress. Therefore, to enhance the temperature sensing accuracy, this potential difference Ve due to stress must be compensated for.
In the conventional pressure sensing device, the temperature sensing bridge circuit is formed on the semiconductor substrate in the position where the stress sensitivity is most impaired. Nevertheless, some stress is inevitably applied to the temperature sensing bridge circuit.
As a result, the application of stress varies the resistance values of the resistance elements for temperature sensing. Then, the potential difference Ve between junctions is varied even if the temperature does not actually change.
For this reason, when stress is applied, the potential difference Ve is caused even when no temperature change occurs. As a result, it is difficult to accurately compensate for temperature variations in output values.